02 Integrated Flood and Inundation Management Strategies for HCMC Mar 2012_ HLP

8/2/2019 02 Integrated Flood and Inundation Management Strategies for HCMC Mar 2012_ HLP

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ntegrate oontegrate oo anan nun at onnun at on

Management Strategies forManagement Strategies for HCMCHCMC::

thethe need andneed and urgencyurgency

Ho Long PhiHo Long Phi

Project DirectorProject Director

HCMC, 7HCMC, 7 --22-- 20122012


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Available Master plansAvailable Master plans

Uncerta nt esUncerta nt es

Integrated Flood Management StrategyIntegrated Flood Management Strategy Expected outcomes of the projectExpected outcomes of the project


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OverviewOverview


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Hydrological impactsHydrological impacts

Upstream flood ps ream oo

Local rainfall

Tidal effect andsea level rise


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Flooded sitesFlooded sites

2003

2011

Local interventions have improved the urban inundation remarkably.


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Urban Flood in Ho Chi Minh CityUrban Flood in Ho Chi Minh City

35180

Count of Flood sites

20

25

30

80

100

120140

160

Count of rainfallevent with volume

> 50mm

Water level

0

5

10

0

20

40

60

2003 2004 2005 2006 2007 2008 2009 2010 2011

Year

Central districts Recently Urbanized Districts Z (cm) R>50mm

The flooding situation in central districts has been improvedsince 2007, thank to drainage system upgrading.

New flooded sites are developing in new urbanized districts.


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Lowland area (


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Available Master PlansAvailable Master Plans


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Master Plan 2001 (PCI)Master Plan 2001 (PCI)752/ 752/ --TTTT 1919--66--20012001

650 km2 of HCM City involving 6 sub-catchments was considered in the master plan 2001.

Mostly to upgrade discharge capacity of storm sewer system + land up-filling.

Abnormalities of hydrological data and urbanization required revision.


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Tide Control Project 2008 (MARD)Tide Control Project 2008 (MARD)-- -- --

The polder system to protect HCMC from SLR

(Phase 1)(Phase 1)

12 largest tide gates and 170 km of dike; under design phase.12 largest tide gates and 170 km of dike; under design phase.

Implementation cost would be 4Implementation cost would be 4--6 folds of original estimation6 folds of original estimation

Land subsidence was not considered.Land subsidence was not considered.


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IU CHNH QUY HOCH CHUNG XY DNG THNH PH H CH MINHN NM 2025

Spatial Plan of HCMC toward 2025- - - TP H CH MINH

Urban drainage zoning Zoned solutions:

Zone B- Zone A: urban drainage system andwater works upgrade

Zone A

- Zone B: Open channels upgrade +Building ground elevation 2,00 m

- Zone C: Only non-structuralmeasures.


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Sea dike?Sea dike?

In 2011, an initiation of super dike is suggested by MARD.


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Project Urban drainage Tide control Land up-fill Zoning

JICA 2001 Yes Small scale Small scale Development stage

MARD 2008 N/A Large scale Zone 2 only River

Sea dike N/A Large scale No No

Almost 1 USD BN has been invested for projects following the master plan 2001.

All available master plans mostly focused on Protection measures of limited design

cr ter a, ac ng o repare ness an , t ere ore, w e vu nera e y extreme events.

Even all approved by Prime Minister, the temporal and spatial harmonies amongthem are ver weak.


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The UncertaintiesThe Uncertainties


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RainfallRainfall

160

180

Yearly max Rainfall eventTan Son Hoa station

80

100120

140

ax(mm)

y = 0.777x - 1453.5

0

20

40X

Year

Volume of yearly-max rainfall events increased about 50mm upon the past 50 years.

Counts of rainfall events with volume >100mm

Period 1952-1961 1962-1971 1972-1981 1982-1991 1992-2001 2002-2011

Counts 0 1 2 2 4 11


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Return frequency changesReturn frequency changes

Moving Average of Return Frequency

y = 0.0383x + 0.14051

1.2

cy

y = 0.02x + 0.0514

0.4

0.6

.

Retu

rnFreque

R>100mm

R>115mm

R>130mm

y = 0.0135x + 0.04190

0.2

Period


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Counts of tidal inundationCounts of tidal inundationCounts of water level X

Phu An station

100

120

40

60

80

counts

120

130

140

145

-20

0

20

1975 1980 1985 1990 1995 2000 2005 2010

year

Counts of water leve l X

Thu Dau Mot station

250

300

Counts of water level X

Nha Be station

250

300

50

100

150

200

counts

>89 cm

>99 cm

>109 cm

>119 cm

>129 cm

>139 cm

>144 cm50

100

150

200

counts

>89 cm

>99 cm

>109 cm

>119 cm

>129 cm

>139 cm

>144 cm

-50

0

1975 1980 1985 1990 1995 2000 2005 2010

year

-50

0

1975 1980 1985 1990 1995 2000 2005 2010

year


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Land subsidenceLand subsidence

Land subsidence is processing strongly in urbanized areas with

average rate of 1.5 cm/yr


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U stream floodU stream floodMax discharge flow from upstream reservoirs to Dong Nai and Sai Gon rivers

3000

3500

)

1500

2000

hargeflow

(m3/

Discharge flow to Dong Nai river

Discharge flow to Sai Gon river

0

500

1000Dis

Year


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Sea level riseSea level rise

Source: ICEM

Sea level rise with average rate of 0.5 cm/yr would endanger 60% of HCMC in 2050


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What to do?What to do?

Sea level rise

subsidenceUpstream

Predictable?Urbanization Rainfall

: onven ona approac


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BangkokBangkok vsvs HCM CityHCM City

Bangkok HCM City

Elevation -2.5 to 3.5 -0.5 to 20

Population(2010) 12,000,000 8,000,000Maz water level(m) -1.5 to +1.65 -1.3 to + 1.57

Land subsidence stable Increasin

Upstream reservoirs yes yes

Low land urbanization High Low


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Ban kok Flood 2011Ban kok Flood 2011

e ups ream reservo rs were a u , unexpec e y ex reme ra a spe screated Bangkok disaster.


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On 13/11/2011, 31/50 Bangkoksdistricts were flooded.

most important metropolitant.


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,

930 industrial complexes , 600.000 jobs endangered.

$ Bn 45 lost; 72 required for recovery; 1.5% GDP lowered.


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Extreme hazard?Extreme hazard?

Catchment rainfall volume was 40% higher than 30-year average, still comparable to1942, 1953 and 1970 events. Why the damage was so extreme?


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Protection strategyProtection strategy

BangkokBangkok vsvs HCM CityHCM CityThe polder system to protect HCMC

from SLR

(Phase 1)(Phase 1)

. Bangkoks system is even better with higher protection level and 15 sub-polders.


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ItemBangkok Ho Chi Minh City

Protecton level 30 year < 1 year < 20 year

Dike 75.8km ++ < 30km 172km

Pumping capacity158 stations(1531 m3/s)

32 station(11 m3/s)

?

15-(168 km2)

Urban detention ponds21

(12.75 triu m3)0 ?

Storm sewer 6404 km 1500 km ?

Protection elevation (m) +2.5 - 3 < 2 +2.5 - +3

Ho Chi Minh city after the project 1547 finished would not be safer than Bangkok 2011.


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Extreme hazard surpassed protection level.Extreme hazard surpassed protection level.

IrrigationIrrigation--oriented reservoir operationoriented reservoir operation..

After 1995, theAfter 1995, the overconfidence created by Flood control systemoverconfidence created by Flood control system

has encouraged urbanization and industry development in floodhas encouraged urbanization and industry development in floodprone.prone.

..

Conflicts in information and response governance.Conflicts in information and response governance.


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Climate change?Climate change?

2025?

2007

Z = 60cmR = 185mm

2015Z =160cm

R = 105 cm

Ho Chi Minh city with tide control would not be safe under extreme storm.


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Flooding volume (Flooding volume (MnMn mm33))

n en ra sun en ra su --ca c menca c menWith land subsidence (water level controlled at 1.0m)

om nat on = mm = mm = mm = mm = mm = mm

Z 0.01 0.39 1.06 2.06 2.94 3.79Z-20cm 0.02 0.55 1.41 2.40 3.27 4.14

- . . . . . .


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Inte rated FloodInte rated Flood--InundationInundation

Management strategyManagement strategy


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for urban flood management HCMCfor urban flood management HCMC

Tide controlTide control system may play an important role but not adequate neither topsystem may play an important role but not adequate neither top..

LandLand subsidencesubsidence as a major factor to accelerate urban flood in HCMC was notas a major factor to accelerate urban flood in HCMC was notappropr ate cons ere .appropr ate cons ere .

There are stillThere are still gaps amonggaps among JicaJica master plan, the tide control project and the Spatialmaster plan, the tide control project and the Spatial

planning to 2025, rising controversial issuesplanning to 2025, rising controversial issues..

Mitigation and ResilienceMitigation and Resilience measures have not been considered appropriately.measures have not been considered appropriately.


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Integrated strategy of urban flood management

Reduce risk from original

o prov e sa ety or

people at appropriatelevel.

Protection Resilience

Risk reduction not hazard

Mitigation and Resilience components.

-

variation and should be decided by a Robust Decision Support System.


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ontro y construct on

Control by flood resilience measures


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Risk mapRisk map

Exposure determines loss

Flood depth and duration

Loss may be of verylarge spatially variation .

may a so vary spat a y.


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frequency, but increase exposure and vulnerabilityfrequency, but increase exposure and vulnerability

Larger construction mayLarger construction maynot provide Flexibilitynot provide Flexibilitytotoa apt w t uncerta nt es.a apt w t uncerta nt es.

Larger construction imposesLarger construction imposes profound impacts onprofound impacts onenvironment and often irreversibleenvironment and often irreversible..


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Expected features of theExpected features of the

Integrated flood management strategyIntegrated flood management strategy

scenarios,scenarios, not protectionnot protection--biasedbiased..

Improving quantification byImproving quantification bybetter simulationbetter simulation

Better implementation byBetter implementation byproject prioritizationproject prioritization andand..

ev ew o ava a e mas er p ans o see aev ew o ava a e mas er p ans o see a emporaempora --

spatial harmonyspatial harmony..


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The urgency of anThe urgency of an

Integrated flood management strategyIntegrated flood management strategy

Available master plans have been implementedAvailable master plans have been implementedconcurrently without harmonyconcurrently without harmony..

The reThe re--consideration ofconsideration offlood prone developmentflood prone development..

TheThe resource competitionresource competition vsvs budget availabilitybudget availabilityin thein the

middle of economic crisis.middle of economic crisis.

Polder or Sea dike? .Polder or Sea dike? .


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plans based on insightful data, tools,plans based on insightful data, tools,..

compre ens ve strategy an scenar o ana ys scompre ens ve strategy an scenar o ana ys s

A robust decision makingA robust decision making


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..

Hazar s may not e a ways prevente , F ooHazar s may not e a ways prevente , F oo

resilience must be emphasized.resilience must be emphasized.

Sta ed intervention ma rovide better flexibilitSta ed intervention ma rovide better flexibilit

to adapt with climate change.to adapt with climate change.


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y u y uy u y u

[email protected]

HP: 0913.721 272

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02 Integrated Flood and Inundation Management Strategies for HCMC Mar 2012_ HLP

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